Assuring Separation of Safety and Non-safety Related Systems

Safety standards call for the separation of safety and nonsafety related systems. Although good guidance is provided in these standards on how to achieve the required hazard analysis, safety integrity assignment and validation to prove a safe system, there is little available on establishing safety boundaries around the critical components and the proof of isolation from non-safety functions. Delineation between safety and non-safety systems is particularly important where it is impractical to substantiate a Safety Integrity Level of the overall system due to the complexity of some components. In this case it is better to assume high failure probability of the nonsafety system and prove isolation from the safety-related system. This paper explores a conceptual methodology (including the use of Fault Tree Analysis and Common Cause Failure Analysis) for establishing and assuring separation of systems and some examples from training simulators that are an example of this situation drawn from real-life. .